STRESS REDUCTION IN MULTI-LAYER STRUCTURES

摘要

1492808 Semiconductor devices; lasers WESTERN ELECTRIC CO Inc 12 Nov 1974 [12 Nov 1973 25 April 1974] 48843/74 Headings H1K and H1C Gallium arsenide layers and epitaxially grown aluminium gallium arsenide layers are substantially lattice-matched at the growth temperature, but on cooling to room temperature difference in thermal expansion coefficients lead to mismatch and consequential stress, particularly undesirable in the case of double heterojunction lasers. According to the invention, phosphorus added to the growth layer introduces slight mismatch at the growth temperature, but by selecting the correct proportion of phosphorus in relation to aluminium and gallium, a substantially stress-free structure is obtained at room temperature. It is shown that when the first layer is Al x Ga 1-x As, wherein x may be O, and the second layer Al y Ga 1-y As 1-z P z , the stress in the second layer at room temperature is less than 2 x 108 degrees/ cm.2 when z/(y-x) lies between 0À03 and 0À05, and is substantially zero when it equals 0À04. The double heterostructure laser shown comprises a Si doped n-GaAs substrate 10, a Te doped n-Al y G 1-y As 1-z P layer 12, a Ge doped n- or p-GaAs layer 14, a Ge doped p-Al q Ga 1-q As 1-p P p layer 16 wherein for a symmetric wave guide y=q and z=p, and a Ge doped p-GaAs layer 18, optionally having a higher conductivity surface formed by diffusion of Zn. The phosphorus content of layers 12, 16 is selected to meet the requirements above, whereby junctions 13, 15 are substantially stress-free at the working temperature of the laser. Contacts 20, 22 are deposited and a resonator is formed by mirrors 24, 26, typically cleavage faces of the crystal. Heat sinks may be associated with the assembly. Current applied to contact 20 may be confined to zone 30 lying between high resistivity zones formed by proton bombardment to the depth of junction 13.